1. Field of the Disclosure
The present disclosure relates to an antenna apparatus, and more particularly relates to (but not in the sense of being limited to) a MIMO antenna apparatus and a wireless communication apparatus implementing such.
2. Description of Related Art
Services called LTE (Long Term Evolution) are being initiated by some communication business operators (operators) as a high-speed data communication specification for mobile phones. When seen from a technical perspective in terms of antennas, LTE has characteristics like the following.
Namely, LTE is a communication system called MIMO (Multi Input Multi Output), which realizes high-speed data communication by using a plurality of antennas to send and receive signals. In portable terminals implementing MIMO, ordinarily two antennas are used. It is sought that the two antenna characteristics ideally be equal.
With regard to antenna characteristics, an indicator called the antenna correlation becomes a key point. Communication speed lowers if the numerical values (coefficients) of antenna correlation are high (in other words, the degree of correlation is high).
Currently, it is desired that the frequency band used by LTE services scheduled in respective countries be extended over a wide range, and that the low bands and high bands of current cellular systems be widened.
For example, in the United States services in the 700 MHz band are scheduled to be initiated, but lowering correlation in the 700 MHz band becomes a significant difficulty. The reason for this is because high-frequency current flows throughout the mobile terminal board as the frequency lowers, becoming an operational mode similar to a dipole, and antenna directionality stops being very dependent on the antenna design. Thus, even if it is attempted to improve correlation by modifying the design of one of the antennas to change the directionality, obtaining desired results is very difficult.
In Japanese Unexamined Patent Application Publication No. 2008-17047, a multi-antenna applicable to a mobile communication system with low mutual coupling effects is proposed. This multi-antenna is provided with plural feed elements respectively coupled to plural feed points on a circuit board, as well as a single or plural non-feed elements coupled to the circuit board in the vicinity of an arbitrary feed point.